It is known to form components utilizing polymers and in particular curable polymers in a wide number of industries and in relation to a wide range of components. Traditionally, other than with regard to thin components, the normal techniques for producing a cured polymer component is either through a two part solvent based or resin based polymer curing process or through use of heat to activate curing of the polymer.
With regard to the solvent and two part processes, activation is typically achieved through a lay up of the solvent based or two part (resin and hardener) polymer combinations within a mould and then heat in applied to activate and accelerate the curing procedure until a desired finished component structure is achieved. Other techniques as indicated to stimulate curing of polymers include simply applying heat possibly delivered through an external source such as within an oven or utilizing infrared heat or utilizing dyes or selected filters within the resin to react with light or heating with microwaves or applying electric current to conductive fibers including carbon fibers to generate heat or chemical reaction heat or utilizing a trigger catalyst which may be triggered by a particular frequency of light. There are also chemical methods, which may delay the curing process to allow assembly of uncured components before the curing reaction completes. Finally, it is also known to coat reinforcing fibers with a catalyst, which again will start curing when combined with the polymer or resin.
A particular problem with such traditionally chemical or heat curing is that, during the curing process, the fiber reinforced polymer shrinks. Shrinkage is usually restrained by fiber stiffness and also by mould shape where applicable. Shrinkage is as a result of molecular changes in the polymer as it changes from an amorphous liquid to a more stabilized solid and also, particularly when solvents are used release of volatiles from the cured polymer. It will also be understood that the curing process is often performed at elevated temperatures and in any event the curing process itself may be exothermic that is to say releases further heat as a result of the molecular changes. In such circumstances as the component cures and then cools residual tensile stresses build up within the component leading to particularly compressive residual stresses at the surface and within the fibers. The tensile residual stresses can lead to matrix cracking and leave the components susceptible to early tensile or fatigue failure. It will be understood that the fibers are essentially string like and therefore are substantially stronger in tension than compression. Compressive residual stresses in fibers allow them to buckle in situ which in turn reduces component stiffness and predisposes the reinforcing fibers to failure in bending. It will also be understood that with relatively thin components incorporating particularly reinforcing weave patterns that shrinkage can occur generally within one axis. This shrinkage may be further exacerbated by moulding pressure in the axis of shrinkage and can result in an anisotropic material performance. This is not always desirable.
In view of the above, it will be appreciated that shrinkage in the polymer matrix during curing is detrimental so that reduction in shrinkage as well as fiber buckling has advantages.
It is known that some ultraviolet curable polymers currently available have no or limited shrinkage upon stability and forming. Unfortunately, by their nature, ultraviolet curable polymers must be exposed to ultraviolet to be cured and in such circumstances formation of thicker components is therefore difficult. It will be appreciated that ultraviolet light will only penetrate to a certain depth. With regard to opaque components or components incorporating opaque fibers for reinforcement, ultraviolet curing to a significant depth through surface exposure is not possible.